CONTACT FORCE SENSOR FOR ABLATION DEVICES CROSS REFERENCE TO RELATED APPLICATIONS

[001] This application claims priority to U.S. Provisional Application Serial no. 61/951,790, filed March 12, 2014, and U.S. Provisional Application Serial no. 61/971,314, filed March 27, 2014, the entireties of which are incorporated herein by reference.

FIELD OF THE INVENTION

[002] Embodiments disclosed herein relate to a contact force sensor for ablation devices. In particular, embodiments disclosed herein relate to a micro-electromechanical systems (MEMS)-based force-sensing cell and its integration with an ablation device such as e.g., an ablation catheter.

BACKGROUND

[003] An ablation procedure refers to a minimally invasive surgical procedure that involves either the destruction or removal of diseased or unnecessary tissue with the goal of curing the disease. An ablation procedure provides a successful surgical alternative that is gradually becoming a popular alternative to invasive procedures amongst physicians and patients. The principal advantages an ablation procedure has over surgery include: shorter recovery times, shorter scars (in length), lower risk of infection, less blood loss, and shorter hospital stays.

[004] Atrial Fibrillation (AF) is the most common form of irregular heartbeat. It is a serious condition affecting 2.66 million people in the United States each year. Given that Atrial Fibrillation occurs more frequently as populations age, the Center for Disease Control (CDC) estimates that a longer living population will drive the number of Americans with Atrial Fibrillation to as many as 12 million annually by 2050. [005] Drugs are most commonly used to treat Atrial Fibrillation. However, catheter ablation (i.e., the use of catheters to deliver radio frequency energy or refrigerant to damaged heart tissue) is becoming the standard of care in tough-to-treat cases.

[006] Traditional catheter ablation techniques encounter challenges based on isolating the pulmonary veins and ablating atrial tissue with the focal catheter. These challenges include: difficulty in maintaining position due to cardiac contractions; variable patient anatomy; variable atrial tissue depth; no direct visualization of the area; and varied catheter force in all directions. Moreover, a successful procedure requires contiguous lesions, which are also a challenge using a catheter ablation technique.

[007] Catheters based on impedance have shown low productivity. Current force-sensing catheter technologies including spring-coil technologies and optical fiber wavelength technologies. The force-sensing catheter technologies, however, are not without their shortcomings. For example, the spring-coil technology is not capable of obtaining directional forces or force distribution that would be beneficial in a catheter ablation procedure. The optical fiber technology has the potential drawbacks relating to being bulky, its optical setup (i.e., lasers, photodetectors, etc.) and the potential problems with the laser source and alignment.

[008] Accordingly, there is a need and desire for a better force-sensing technique for use with an ablation device, such as a e.g., catheter ablation device (also referred to herein as an ablation catheter).

SUMMARY

[009] Embodiments disclosed herein provide a micro-electromechanical systems (MEMS)- based force-sensing cell for an ablation device. In one embodiment, a plurality of force- sensing cells are provided on and around an ablation catheter body forming a force-sensing ablation catheter. BRIEF DESCRIPTION OF THE DRAWING

[010] Figure 1 illustrates a cross-sectional view of an example force-sensing cell constructed in accordance with the disclosed principles.

[Oi l] Figure 2 illustrates a top-down view of the force-sensing cell illustrated in Figure 1.

[012] Figure 3 illustrates the example operating principles of the force-sensing cell illustrated in Figure 1.

[013] Figures 4A-4F illustrate an example fabrication process of a portion of the Figure 1 force-sensing cell.

[014] Figure 5 illustrates an example contact force-sensing ablation catheter constructed in accordance with the disclosed principles.

[015] Figure 6 illustrates an example view of sockets to be used on a side portion of the ablation catheter body illustrated in Figure 5, the sockets being suitable for receiving the force-sensing cells of Figure 1.

[016] Figure 7 illustrates an example view of sockets to be used on a tip portion of the ablation catheter body illustrated in Figure 5, the sockets being suitable for receiving the force-sensing cells of Figure 1.

DETAILED DESCRIPTION

[017] In the following detailed description, a plurality of specific details, such as types of materials and dimensions, are set forth in order to provide a thorough understanding of the preferred embodiments discussed below. The details discussed in connection with the preferred embodiments should not be understood to limit the claimed invention. Furthermore, for ease of understanding, certain method steps are delineated as separate steps; however, these steps should not be construed as necessarily distinct nor order dependent in their performance. [018] The embodiments disclosed herein provide a force-sensing device, referred to herein as a "force-sensing cell" or FC. Multiple force-sensing cells will be provided on an ablation catheter to create a contact force-sensing ablation catheter. The disclosed contact force- sensing ablation catheter will allow e.g., a cardiovascular surgeon to better navigate through the heart during an ablation procedure because the disclosed embodiments use novel force- sensing micro-electromechanical systems (MEMS) sensors and/or micro-electrode systems to simultaneously measure multiple directions and angles of pressure. Furthermore, the MEMS- based sensors not only measures force but also tissue properties based on impedance.

[019] In accordance with the disclosed principles, the force-sensing will be achieved using a MEMS-based carbon strain sensor on a flexible substrate that will have a piezoresistive characteristic. It should be appreciated that the signal from the MEMS-based sensors can travel through a cable to a juncture box and/or monitor screen displaying a graphical user interface (GUI) assisting with electrical mapping. The signals from the disclosed force- sensing ablation catheter assists the surgeon by informing the surgeon: 1) where the catheter is to avoid puncturing heart tissue; 2) what lesion size to create; and 3) where to avoid creating clots and thrombosis.

[020] As is discussed below in more detail, the disclosed force-sensing cell utilizes a polymer-based carbon-sputtered thin film to detect the contact force. The carbon-sputtered film will exhibit the piezoresistive characteristic as described in U. Tata, H. Cao, C. M. Nguyen, and J.-C. Chiao, "Flexible Sputter-Deposited Carbon Strain Sensor," IEEE SENSORS JOURNAL, vol. 13, pp. 444-445, 2013. The cell can be embedded on the tip as well as the side walls of the ablation catheter, thus enabling simultaneous multi-site contact force-sensing.

[021] Figure 1 illustrates a cross-sectional view of the MEMS-based force-sensing cell 10 constructed in accordance with the disclosed principles. The illustrated cell 10 comprises a cover 12 provided over a stopper 14 that is provided on a sensing element 16. Connection leads 18 are connected to the sensing element 16 by a conductive adhesive 20 such as e.g., a conductive epoxy. Figure 2 illustrates a top-down view of the force-sensing cell 10 showing the approximate locations of the leads 18 and stopper 14 in phantom.

[022] In one embodiment, the cell 10 will have a size of approximately 1x0.5 mm ² and the connection leads 18 will be approximately 2.0 mm long. The leads 18 are for connecting the cell 10 to a processing circuit (not shown) and to transmit sensed force data to the circuit. Moreover, the leads 18 will anchor the sensing element 16 so that contact force F will be translated to strain information (discussed in more detail with respect to Figure 3). The stopper 14 acts as a bump so that the contact force F is easily applied to the cell 10. As discussed below in more detail, in one embodiment, the stopper 14 will be made of photoresist material (e.g., SU-8 photoresist) by a conventional photolithography process. In one embodiment, the stopper 14 will have a diameter of 200 μιη and a thickness of 50 μιη. In one embodiment, the cover 12 is a thin (e.g., approximately 2-5 μιη) flexible polymer such as e.g., silicone, polyimide or parylene C. It should be appreciated that the disclosed embodiments are not limited to any particular size, length or thickness of the cell 10 or its components.

[023] Referring to Figures 1 and 3, when a contact force F is applied to the cell 10, the cover 12, stopper 14 and sensing element 16 will move downwardly in the direction of the arrow (example downward positioning of the stopper 14 and sensing element 16 is shown in phantom). As shown in Figure 3, this force F (box 31) causes a strain or bending of the cell 10 (box 33), which changes the resistance R and/or capacitance C of the cell 10 (box 35). This change in resistance R and/or capacitance C will be detected by the processing circuitry (via the leads 18) (box 37) and used during the medical procedure as discussed herein.

[024] Figures 4A-4F illustrate an example fabrication process of a portion of the force - sensing cell 10 constructed in accordance with the disclosed principles. Figure 4A illustrates a substrate 401 upon which the various layers of the cell 10 will be fabricated. One desirable substrate 401 includes a silicon wafer such as e.g., a hexamethyldisilazane-treated (HMDS) silicon wafer. As shown in Figure 4B, a layer 403 of nickel (Ni) is formed over the substrate 401. In one embodiment, the layer 403 is deposited on the substrate 401 and is approximately 0.1 μιη thick. Then, a layer 405 of carbon (C) is formed over the layer 403 of nickel. In one embodiment, the carbon layer 405 is deposited by RF magnetron sputtering of a graphite target using a e.g., a sputter plant at 150-W of power for a period of e.g., 8 hours. In one embodiment, the carbon layer 405 is approximately 0.5 μιη thick. At this point, the substrate 401 and the two layers 403, 405 can be annealed at e.g., 1000°C for about 1 hour to enhance the carbon's film quality.

[025] As shown in Figure 4C, a layer 407 of parylene C will be formed over the carbon layer 405. In one embodiment, the parylene C layer 407 will be coated onto the carbon layer 405 and will be approximately 5μιη thick. As shown in Figure 4D, the parylene C layer 407 will be patterned by e.g., an oxygen plasma process. The patterned the parylene C layer 407 will define the sensing element area 409. In one embodiment, the size of the sensing element area 409 will be approximately 1x0.5 mm ² . Holes 411 will be provided for the connection leads. In one embodiment, the holes 411 will have a diameter of approximately 60 μιη.

[026] As shown in Figure 4E, a layer of photoresist material will be formed on the sensing element area 409 and then patterned to form the stopper 14 approximately positioned in the middle of the sensing element area 409. In one embodiment, the photoresist material will be SU-8 photoresist material. As shown in Figure 4F, the carbon layer 405 is etched by e.g., a dry etch process using e.g., carbonyl sulfide and the nickel layer 403 is removed by e.g., a wet etchant process. The remaining structure 413 containing a thin film carbon on the parylene C membrane is then released from the substrate 401 and can now be used as the basis for the sensing element 16 and stopper 14 illustrated in Figure 1.

[027] Figure 5 illustrates an example contact force-sensing ablation catheter 500 constructed in accordance with the disclosed principles. The contact force-sensing ablation catheter 500 includes a conventional ablation catheter body 501 suitable for performing an ablation procedure. The disclosed catheter 500 also has a plurality of force-sensing cells 510 formed around the side portions of the catheter body 501 and a plurality of force-sensing cells 520 formed on the tip of the body 501. The plurality of force-sensing cells 510, 520 are constructed as shown in Figure 1.

[028] In accordance with the disclosed principles, the force-sensing cells 510 formed around the side portions of the catheter body 501 provide lateral force detection while the force- sensing cells 520 formed on the tip of the catheter body 501 detects force distribution. This innovative design will increase the spatial resolution of force-sensing and make the catheter 500 as sensitive as a human finger. In the illustrated embodiment, the force-sensing cells 520 formed on the tip of the catheter body 501 are arranged in an array of four cells. It should be appreciated, however, that any number of force-sensing cells 510 can be formed around the side portions of the catheter body 501 and that the disclosed embodiments should not be limited to the number of cells 510 illustrated in Figure 5. Likewise, it should be appreciated that any number of force-sensing cells 520 can be formed on the tip of the catheter body 501 and that the disclosed embodiments should not be limited to the number of cells 510 illustrated in Figure 5.

[029] Figure 6 illustrates an example view of sockets 610 used on the side portions of the ablation catheter body 501 illustrated in Figure 5. As can be appreciated, the sockets 610 are suitable for receiving the force-sensing cells 10 of Figure 1. Figure 7 illustrates an example view of sockets 720 used on the tip portion of the ablation catheter body 501 illustrated in Figure 5. As can be appreciated, the sockets 720 are suitable for receiving the force-sensing cells 10 of Figure 1. In one embodiment, the sockets 610, 720 are designed to be universal sockets, meaning that the sockets 610, 720 will be able to receive the cells 10 and other sensors fitting in the socket dimension suitable for integration with the catheter and used for other applications such as impedance sensing, pH sensing, etc.

[030] The disclosed micro-electro-mechanical systems (MEMS) force-sensing cells 10 and force-sensing ablation catheter 500 provide several advantages over today's existing spring- coil or optical fiber force-sensing ablation techniques. For example, structurally, the disclosed cells 10 have a small size specifically designed for use with an ablation catheter. Any size stopper 14 can be used providing a strain sensor. The flexible top of the cells 10 enables other sensing application to be used (e.g., impedance). Simplified wiring, interconnections and circuitry suitable for hollow-guide catheters can also be used.

[031] The fabrication of the cells 10 is also advantageous. As shown above, the disclosed fabrication used carbon deposition and an innovative method to transfer the carbon film from a silicon wafer to a parylene C membrane. The disclosed principles can be used with other catheter ablation applications such as e.g., cardiac Maze surgery or electric cardioversion; cancer/tumor ablation; ophthalmology; urology; gynecology; or orthopedics ablation procedures.

[032] The disclosed principles can be uses with other technologies besides radiofrequency technologies. These include e.g., thermal technologies such as electrical ablators and electronic brachy therapy; intensity modulated radiation therapy, image guided radiotherapy, stereotactic radiotherapy (SRT), stereotactic body radiation therapy, nano-radiation therapy and proton beam therapy; cold lasers, excimer lasers and ultraviolet B lasers; temperature controlled devices, fluid cooled device and robotic navigation-catheter manipulation systems; HIFU (High Intensity Focused Ultrasound), Magnetic Resonance Imaging- Guided Focused Ultrasound; microwave thermo therapy; endometrial hydrothermal balloon ablation devices; and laser based procedures. The disclosed principles can also be used for non-thermal procedures such as a tissue contact probe, cryogen spray probe and epidermal and subcutaneous cryoablation devices; or hydromechanical devices/procedures.

[033] As noted above, the annealed carbon thin film on the flexible parylene C membrane will exhibit a piezoresistive characteristic, thus a simple bridge set up could be used to interpret the data as described in U. Tata, H. Cao, C. M. Nguyen, and J.-C. Chiao, "Flexible Sputter-Deposited Carbon Strain Sensor," IEEE SENSORS JOURNAL, vol. 13, pp. 444-445, 2013. In the disclosed catheter embodiment, this simple circuit can be placed outside of or integrated monolithically within the force-sensing cell with conventional microfabrication techniques. It should be appreciated that the disclosed contact force-sensing technology is not limited to a cardiovascular tool and that the disclosed contact force-sensing technology may be used with/for robotic surgery where surgeon's desire to get a feel for a procedure being performed with robot-assisted tools.

[034] The foregoing examples are provided merely for the purpose of explanation and are in no way to be construed as limiting. While reference to various embodiments is made, the words used herein are words of description and illustration, rather than words of limitation. Further, although reference to particular means, materials, and embodiments are shown, there is no limitation to the particulars disclosed herein. Rather, the embodiments extend to all functionally equivalent structures, methods, and uses, such as are within the scope of the appended claims.

[035] Additionally, the purpose of the Abstract is to enable the patent office and the public generally, and especially the scientists, engineers and practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection the nature of the technical disclosure of the application. The Abstract is not intended to be limiting as to the scope of the present inventions in any way.